The present invention relates to magnetic flowmeters that sense the flow of process fluid in industrial process plants. More specifically, the present invention relates to measurement of flow using a magnetic flowmeter.
Magnetic flowmeters are known in the art and utilized electrically insulated flow tube that carries a flow of process fluid past a coil of an electric magnet and past electrodes. The electrode magnet applies electromagnetic field to the flowing process fluid. Due to Faraday's Law of electromagnetic induction, a voltage or Electro Mode of Force (EMF) is generated between a pair of electrodes in the fluid. This voltage is a function of the strength of the applied magnetic field and is proportional to the rate of flow of the fluid.
The sensed voltage is proportional to the volumetric flow rate of process fluid through the flow tube. However, mass flow rate is related to both the density of the fluid as well as its velocity. Mass flow rate can be calculated by multiplying the density of the fluid velocity and the cross sectional area of the flow tube. However, for many fluids, fluid density is related to the temperature of the fluid. In order to use a typical magnetic flowmeter to measure mass flow, a separate temperature sensor must be utilized to perform the mass flow calculation.